﻿//
// Created by alex on 2022/5/29.
//

/*
 * Copyright (c) 2018, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <ctime>
#ifndef _WIN32
#include <sys/time.h>
#endif

 /* This is a safe version of localtime() which contains no locks and is
  * fork() friendly. Even the _r version of localtime() cannot be used safely
  * in Redis. Another thread may be calling localtime() while the main thread
  * forks(). Later when the child process calls localtime() again, for instance
  * in order to log something to the Redis log, it may deadlock: in the copy
  * of the address space of the forked process the lock will never be released.
  *
  * This function takes the timezone 'tz' as argument, and the 'dst' flag is
  * used to check if daylight saving time is currently in effect. The caller
  * of this function should obtain such information calling tzset() ASAP in the
  * main() function to obtain the timezone offset from the 'timezone' global
  * variable. To obtain the daylight information, if it is currently active or not,
  * one trick is to call localtime() in main() ASAP as well, and get the
  * information from the tm_isdst field of the tm structure. However the daylight
  * time may switch in the future for long running processes, so this information
  * should be refreshed at safe times.
  *
  * Note that this function does not work for dates < 1/1/1970, it is solely
  * designed to work with what time(NULL) may return, and to support Redis
  * logging of the dates, it's not really a complete implementation. */
namespace toolkit
{
	static int _daylight_active;
	static long _current_timezone;

	int get_daylight_active()
	{
		return _daylight_active;
	}

	static int is_leap_year(time_t year)
	{
		if (year % 4)
			return 0; /* A year not divisible by 4 is not leap. */
		else if (year % 100)
			return 1; /* If div by 4 and not 100 is surely leap. */
		else if (year % 400)
			return 0; /* If div by 100 *and* not by 400 is not leap. */
		else
			return 1; /* If div by 100 and 400 is leap. */
	}

	void no_locks_localtime(struct tm* tmp, time_t t)
	{
		const time_t secs_min = 60;
		const time_t secs_hour = 3600;
		const time_t secs_day = 3600 * 24;

		t -= _current_timezone; /* Adjust for timezone. */
		t += 3600 * get_daylight_active(); /* Adjust for daylight time. */
		time_t days = t / secs_day; /* Days passed since epoch. */
		time_t seconds = t % secs_day; /* Remaining seconds. */

		tmp->tm_isdst = get_daylight_active();
		tmp->tm_hour = seconds / secs_hour;
		tmp->tm_min = (seconds % secs_hour) / secs_min;
		tmp->tm_sec = (seconds % secs_hour) % secs_min;
#ifndef _WIN32
		tmp->tm_gmtoff = -_current_timezone;
#endif
		/* 1/1/1970 was a Thursday, that is, day 4 from the POV of the tm structure
		 * where sunday = 0, so to calculate the day of the week we have to add 4
		 * and take the modulo by 7. */
		tmp->tm_wday = (days + 4) % 7;

		/* Calculate the current year. */
		tmp->tm_year = 1970;
		while (1)
		{
			/* Leap years have one day more. */
			time_t days_this_year = 365 + is_leap_year(tmp->tm_year);
			if (days_this_year > days)
				break;
			days -= days_this_year;
			tmp->tm_year++;
		}
		tmp->tm_yday = days; /* Number of day of the current year. */

		/* We need to calculate in which month and day of the month we are. To do
		 * so we need to skip days according to how many days there are in each
		 * month, and adjust for the leap year that has one more day in February. */
		int mdays[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
		mdays[1] += is_leap_year(tmp->tm_year);

		tmp->tm_mon = 0;
		while (days >= mdays[tmp->tm_mon])
		{
			days -= mdays[tmp->tm_mon];
			tmp->tm_mon++;
		}

		tmp->tm_mday = days + 1; /* Add 1 since our 'days' is zero-based. */
		tmp->tm_year -= 1900; /* Surprisingly tm_year is year-1900. */
	}

	void local_time_init()
	{
		/* Obtain timezone and daylight info. */
		tzset(); /* Now 'timezome' global is populated. */
#if defined(__linux__) || defined(__sun)
		_current_timezone = timezone;
#elif defined(_WIN32)
		time_t time_utc;
		struct tm tm_local;

		// Get the UTC time
		time(&time_utc);

		// Get the local time
		// Use localtime_r for threads safe for linux
		//localtime_r(&time_utc, &tm_local);
		localtime_s(&tm_local, &time_utc);

		time_t time_local;
		struct tm tm_gmt;

		// Change tm to time_t
		time_local = mktime(&tm_local);

		// Change it to GMT tm
		//gmtime_r(&time_utc, &tm_gmt);//linux
		gmtime_s(&tm_gmt, &time_utc);

		int time_zone = tm_local.tm_hour - tm_gmt.tm_hour;
		if (time_zone < -12)
		{
			time_zone += 24;
		}
		else if (time_zone > 12)
		{
			time_zone -= 24;
		}

		_current_timezone = time_zone;
#else
		struct timeval tv;
		struct timezone tz;
		gettimeofday(&tv, &tz);
		_current_timezone = tz.tz_minuteswest * 60L;
#endif
		time_t t = time(NULL);
		struct tm* aux = localtime(&t);
		_daylight_active = aux->tm_isdst;
	}
} // namespace toolkit
